C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Innacurate Tachometer

Old Dec 30, 2008 | 07:28 PM
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Stingray1970
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Default Innacurate Tachometer

I have a 91 that the tach is reading about 3,000 too high. It idles around 3,700 and runs out of numbers if I rev it. Any suggestions will be appreciated.
Thanks,
Gene
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Old Dec 30, 2008 | 07:38 PM
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Originally Posted by Stingray1970
I have a 91 that the tach is reading about 3,000 too high. It idles around 3,700 and runs out of numbers if I rev it. Any suggestions will be appreciated.
Thanks,
Gene
I also have a '91. The tach is reading about 1,600 at idle, but that was after starting it with new injectors, IAC, intake gaskets, rebuilt tranny, etc. So, I started doing some research on this very subject today and found that more '90 model year corvettes have this problem than '91s.

The consensus was that if the idle is erratic, it can be the tachometer filter (located near the firewall behind the driver's side cylinder head). However, if there is a consistent high tach reading, it is likely a rebuild of the instrument panel is needed.

Several people offer the rebuild service - Eckler's, Zip, corvettedashclusterservice.com, http://www.tabercorvetteparts.com/parts/clusters.html.

Tachometer filters for the '90 and '91 are no longer available from any major supplier and salvage yards or private sales seem to be the only source.

I also discovered that the '92 and '93 instrument panel is easily swapped into the '91. I read about a forum member that still had trouble even after rebuilding the gauge cluster and changing the tach filter. He ended up getting a '93 and it worked perfectly!

Also, if you use an aftermarket distributor or coil, I've read there can be problems.

-Jonathan
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Old Dec 30, 2008 | 07:41 PM
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http://forums.corvetteforum.com/c4-g...1990-vert.html

http://www.thirdgen.org/techboard/el...meter-fix.html
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Old Dec 30, 2008 | 09:56 PM
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I really appreaciate the response. I have time as I'm going to strip and paint the car.
Is there a way to bench test the filter? It looks like a capacitor to me.
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